Impacts of Built Environment on Surface and Groundwater in District Peshawar, Pakistan

Abstract

This study analyses the spatio-temporal impact of built environment on surface and groundwater in district Peshawar, Pakistan. The population of district Peshawar has increased from 0.556 million in 1981 to 4.269 million in 2017. Similarly, the built-up area also increased from 3.7 % in 1981 to 16.27 % in 2014 and the projected figure is 22 % by 2030. In the study area, water supply system is fetched almost exclusively from groundwater with over 1400 public and more than 3000 private tube wells, dug wells and hand pumps. In order to achieve the study objectives, data were collected from various sources. For analysis of groundwater status, data were collected from all the union councils (UCs). However, for detailed analysis, eleven union councils were selected from six drainage basins within the district. Parallel to this, 140 tube wells were selected randomly for detailed and intensive analysis of stratigraphy and groundwater. In addition, individual household survey and Focused Group Discussions (FGDs) with stakeholders were conducted in the sample UCs. Structured interviews were also conducted with the officials of the concerned line agencies to cross check and validate the results. Secondary data were acquired from Public Health Engineering Department, Water and Sanitation Services Peshawar, Provincial Irrigation and Drainage Authority, Geological Survey of Pakistan, Soil Survey of Pakistan, Pakistan Meteorology Department, Agriculture Research Institute Tarnab, Provincial Disaster Management Authority, Population Census Organization and Peshawar Development Authority. Multi-spectral Landsat images of 1981 and 1991 were acquired from open source, whereas SPOT images for the year 2009 and 2014 were obtained from SUPARCO and the same were spatiotemporally analyzed for land use land cover classification and mapping. To delineate watershed of rivers and streams, SRTM images were used. The spatial databases were developed in ArcGIS and ERADAS imagine. Curve Number (CN) techniques and models were used for surface runoff and volume calculation. All the six drainage basins were delineated and the watersheds within the district were marked as the urban drainage basins. The analysis revealed that natural groundcover has been gradually replaced by Impervious Surface Cover (ISC) and this steady change is mainly at the cost of consuming fertile agricultural land. In district Peshawar, socio-economic, infrastructural and physical developments are the major intervening factors of land take and surface cover changes. The analysis further revealed that the urban watersheds of rivers and streams have recorded remarkable growth and expansion in term of built environment. This continuous increase in ISC within the urban drainage basins of rivers and streams have further escalated surface runoff and reduced infiltration, seepage and percolation to groundwater. Consequently, in district Peshawar the frequency and intensity of urban and riverine floods have been increased and expected to aggravate in future. Average daily demand of fresh water has been increased from 56 million liters per day (ml/day) in 1981 to 213 ml/day in 2017 which will further rise to 310 ml/day by 2030. The analysis also revealed that the fresh water sources are under constant pressure. Increased rate of extraction from groundwater will have serious implications and can lead to urban drought. The multiplication of soil sealing in the form of built-up areas have halted the aquifers recharge and posed a potential threat to fresh water sources. It was also calculated that the recharge rate through rainwater has been reduced from 108.75 mm/year in 1981 to 91.35 mm/year in 2014, whereas the groundwater discharge is 105 mm/year. This indicates that the rate of groundwater discharge is more than the recharge, which clearly indicate the groundwater depletion especially in the corporation limits. Analysis further reveals that in old city, a number of tube wells have been dried up and deep drilling has been done for the extraction of fresh water. This calls upon the decision-makers to supply fresh water from the rivers, to minimize pressure on the existing groundwater sources and to check the unprecedented conversion of natural ground into impermeable land covers.